| TiAl alloy is considered to be the most promising lightweight structural materials in aerospace, winch has high strength and ductility, creep resistance, excellent oxidation resistance at high temperatures. This paper studied the hot deformation behavior, canned forging numerical simulation, quenching and heat treatment process, microstructure and mechanical properties of Ti-48.5Al-6Nb-6V-0.25Y alloy.The high temperature deformation behaviors of as-cast alloy were investigated at the temperatures ranging from1050to1250℃with the strain rates ranging from e-4to e0s-1, using Gleeble-1500simulator, with60%engineering stain. The true stress-strain curves of hot deformation could be divided into three sections, namely the stage of hardening, the flow softening stage, the steady-state flow stage, which was the result generated by the interaction of the hardening effect and the dynamic recrystallization softening effect. The peak stress of hot deformation decreased with increasing deformation temperature and decreasing strain rate, which could be represented by a hyperbolic sine equation using the Zener-Hollomon parameter. The apparent activation energy value Q and stress exponent n for the cast alloy were measured as361.7892kJ/mol and5.65459.Based on the dynamic material model, the Murty type of processing maps was founded. The power dissipation efficiency η increased gradually with the temperature T increasing and strain rate decreasing, the maximum value nearly at1250℃and e-4s-1, and the minimum nearly at1050℃and e0s-1. The reason was that the driving force of phase transition, recovery recrystallization in the casted alloy was enhanced with the increasing temperature. Another factor was that the time became longer when deformed at lower strain rate, which made phase transition, recovery recrystallization more completely. With deformation temperature increasing and stain rate decreasing, i.e. Z decreasing, dynamic recrystallization became more active. A suitable set of forging processing parameters for the alloy was the deformation temperature above1150℃, and stain rate below e-4s-1. At this condition, the appearance of the deformed specimen was good, with dynamic recrystallization being more adequate and uniform structure and small grain.Based on the former hot compressing data, the TiAl alloy materials database was founded in Deform program. Forging simulation at different temperature and deformation rate with different can thickness was studied. The results showed that the canned forging model was better than the not-canned model and ringed model, which was more conducive to uniform deformation and can significantly reduced the possibility of generating macroscopic destruction. After forging simulation with different can thickness, deformation temperature and deformation rate, a reasonable set of canned forging process parameters were summarized:20mm can thickness,1200or1250℃deformation temperature and0.02s-1strain rate.According to the results of numerical simulation, the cast alloy ingots were forged at the condition of1250℃deformation temperature and0.02s-1strain rate with20mm stainless steel can thickness. The Microstructure, phase composition of the original, quenched and heat treated alloy were respectively analyzed by optical micrograph, SEM micrograph in BSE mode, EDS and XRD. Tensile tests of forged alloy were taken at room temperature and high temperature. Tensile properties and microstructure changes at room temperature and high temperature of forged alloy were studied. Compression properties at room temperature sampled from different locations of forged stock were studied. The study found that the as-cast alloy was nearly y phase microstructure with large grain size, while the wrought alloy also nearly y microstructure with greatly reduced grain size and a small amount of B2phase. Studying on quenched microstructure at the temperature range of1200～1300℃found that,α2phase began to precipitate above1250℃temperature, and precipition content increases with increasing holding temperature. The tensile test found that with temperature increasing, strength decreased, but plastic significantly increased, attributed to the dynamic recrystallization effect strengthening. Temperature compression tests found a significantly different performance based on the distance away from the center and the direction. Sample of normal direction has the best strength and ductility, and radial direction took second palce. The mechanical properties of forged stock were best of the location at r/4-r/2center distance, and worst at more than2r/3. Heat treatment was launched at1350～1430℃Temperature. With increasing temperature, the lamellar precipitation increased, while the casted alloy turned into a duplex microstructure at1390C heat treatment, meanwhile forged alloy at1410℃, which maybe caused by the forging process. |
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